Polymers containing amine functionality are being sought for a variety of potential uses. Such polymers represent a cost effective way of incorporating cationic charge into polymers, for example, for cationic electrocoat polymers, water treating polymers, and additives for enhanced oil recovery. Such amine functional polymers offer potential for superior adhesion to many types of substrates compared to typically neutral or anionic polymers because the functional amine group has a high electron donating ability when unprotonated and a cationic charge when protonated. By changing pH through the addition of either acid or base, these polymers can change properties to offer valuable options for viscosity control, control of emulsion stability, polymer modification for solubility, especially in water, or for a variety of systems for formulating shelf-stable polymers that are nevertheless capable of crosslinking or reacting with various substrates.
The synthesis of amine functional polymers is, however, difficult for at least two reasons. The simplest amine functional monomer, vinylamine, is thermodynamically and kinetically unstable relative to the isomeric Schiff base and condensation products of the base, ethylidine imine. Secondly, more stable allyl- and diallyl/amine monomers are expensive and typically show severe chain transfer during free radical polymerization, especially when involving allyl protons on carbon atoms alpha to the nitrogen atom in the amine. The allylamines are known to produce mainly low molecular weight polymers and copolymers even when using large amounts of free radical initiators.
In addition to having amine functionality, it is desirable that such polymers also be water soluble. It is also desirable to control the level of amine functionality, either to reduce cost by diluting the expensive amine component or for applications in which a lower level of cationic or reactive amine gives superior performance. For such reasons, it is especially desirable to develop polymers of vinyl alcohol which contain low but controlled levels of amine functionality. Other monomers which contain tertiary amine functionality, such as N,N-dialkylethylacrylamides, are expensive and polymerize poorly with vinyl acetate, the precursor to poly(vinyl alcohol).
The preparation of amine functional poly(vinyl alcohol) has been accomplished previously by copolymerizing N-vinyl-0-t-butylcarbamate. N-vinylacetamide, or N-allylurethane with vinyl acetate and then hydrolyzing the polymerized vinyl acetate component with an alcohol, such as methanol or aqueous base, followed by heating an aqueous solution of the copolymer with excess acid for an extended period of time. This procedure produces a relatively dilute aqueous solution of the polymer which is expensive to store or ship and requires expensive additional steps to isolate the polymer from solution. The aqueous solution also contains substantial amounts of undesirable salts or acid.
Copolymerizations of this general nature are illustrated by such references as U.S. Pat. No. 2,748,103 Priest (1956) which discloses copolymerization of vinyl acetate with N-allylurethane followed by hydrolysis of the acetate groups in the copolymer to hydroxy groups.
Brouwer et al., J. Pol. Sci. Pol. Chem. Ed. 22 2353-2362 (1984) discloses the hydrolysis of poly(N-vinyl-tert-butylcarbamate-co-vinyl acetate) in one to one volume mixtures of ethanol and HCl to form a copolymer of vinyl amine and vinyl alcohol. As pointed out by this reference, however, N-vinyl-tert-butylcarbamate is subject on hydrolysis to produce the toxic product, ethyleneimine. It is stated that hydrolysis of the tertiarybutylcarbamate proceeds faster than the acetate, but both are complete within 48 hours.
Stackman et al., Industrial Engineering Chemistry, Prod. Res. Dev. 24 242-246 (1985) discloses copolymerization of N-vinylacetamide with vinylacetate (VA) as well as homopolymerization of N-vinylacetamide (NVA). Hydrolysis of the poly(N-vinylacetamide) produces poly(vinylamine). Also described is the synthesis route to N-vinylacetamide using dimethylacetal and acetamide. Hydrolysis of the copolymer involves only the acetate groups initially. It is stated that hydrolysis of 20:80 NVA:VA copolymer with base went rapidly to 70% completion and then stopped. The hydrolyzed copolymers are said to have formed clear films which were tougher than those from either the unhydrolyzed copolymer or the NVA homopolymer.
U.S. Pat. No. 4,675,360, Marten (1987) describes copolymers of vinyl alcohol with poly(alkyleneoxy) acrylate and describes a method for incorporating these polyalkylene oxide side chains to act as internal plasticizers for polyvinyl alchohol. Conditions are described for copolymerizing vinyl acetate and polyalkylene acrylate monomer using free radical initiation and stripping out the unpolymerized vinyl acetate after polymerization is complete. The polymer is then hydrolyzed in methanol using catalytic alcoholysis to produce the copolymer of vinyl alcohol and poly(alkyleneoxy) acrylate containing potentially unhydrolyzed vinyl acetate groups.